Taco SR506 to Hydrostat 3250 Plus Constant Heat Call
System is indirect water heat, 5 zone hydronic w/Taco circs. I recently had a leaking valve replaced in my boiler system. After, the burner was failing to trigger. The HVAC guy mentioned he noticed the Hydstrostat 3250 temp control showed fluctuations in the temp and suggested replacing it which I did. This should be an on-demand system letting the boiler stay off until there's a call for either heat or hot water but now it's running the boiler at the set 180 deg high and trigger back on at approx 30 deg lower (155-160) bringing it back to 180, wasting oil which at the moment for obvious reasons, don't want to do. The Hydrostat continuously shows a dot bottom right of the current temp indicating a constant call for heat or hot water. I check/tightened all connections on the Taco SR506, turned off power and checked the removable relay "ice cubes" (all except the 120V one) and still shows call for heat. Turned off and physically removed all the basic Honeywell thermostats, still shows call for heat. After replacing the temp control unit for $230, I don't want to replace the Taco SR506 unless I'm sure this will cure the problem. Any & all suggestions would be greatly appreciated!
Comments
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a pic of how you have the taco wired, and the hydrostat wired, might help. sounds like you have something wired wrong at the new hydrostat
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Sounds like this is a new behavior since the Hydstrostat 3250 was changed.
If all the heat demands are through the Taco SR506 and when the Taco SR506 has no active demand for heat yet the Hydstrostat 3250 acts like there is a demand for heat, I would suspect the wiring from the Taco SR506 to the Hydstrostat 3250 was inadvertently changed (or corrupted) causing the " indicating a constant call for heat or hot water ".
I would completely inspect the wiring path between the Taco SR506 X - X terminals and the Hydstrostat 3250 T - T terminals. With the replacement work done maybe the two wires were crushed together somewhere.
Also a test of the Hydstrostat 3250, with the power off, disconnect one of the Hydstrostat 3250 T - T wires then restore the power see it the call for heat has ceased.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System
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Thanks for the reply. I was very careful to replace each wire exactly as on the original Hydrostat. Pic of both the Hydrostat and Taco….
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"Sounds like this is a new behavior since the Hydstrostat 3250 was changed."
I'll try your recommendation though I was VERY careful with the replacement making sure each is correct and tight as was. I disconnected the ZC/ZR wires and this did turn off the call for heat dot on the Hydrostat. That wire goes to the Taco DR501 switching relay (indirect hot water) a separate unit from the Taco SR506 zone pane. On the SR506, zone 6 thermostat terminals are not connected to anything which I believe is that panel's indirect water thermostat.
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In your picture ZC/ZR has no wires, just a jumper. The Taco SR506 X - X (Isolated End Switch) are the wires that go to the Hydstrostat 3250.
Remove one or both of these wires, See if the call for heat goes a way.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System0 -
Bit confused with this " System is indirect water heat, 5 zone hydronic w/Taco circs. " so you have 5 indirect DHW (Domestic Hot Water) tanks ?
Or 1 indirect DHW tank and 4 space heating zones.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System0 -
Is this switch in the same position as the old unit ?
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System0 -
No unintentional connection between these smaller Red and White (ZC/ZR) wires ?
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System
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First, there are wires going to ZC/ZR but that's not what's circled in your picture. You circled TT terminals which I agree comes from the Taco SR506 terminals X/X. I disconnected 1 of the terminals (low voltage) live and it did not eliminate the call for heat dot on the Hydrostat. However, when I disconnected the 2 wires going to ZC/ZR on the Hydrostat, that did eliminate the dot. I believe those 2 wires control the indirect hot water Taco SR501 single zone control.
In the Taco SR506 6 zone controller, there are no wires to the Zone 6 thermostat which is the priority thermostat used for indirect water. There's no wire from the lower section zone 6 for the circ pump either. There is a jumper between ZR/ZC.
Near the indirect water storage tank is a Taco SR501. I'm wondering if the SR506 ZC/ZR is going only to the SR501, never touches the SR506 and the issue keeping the dot on is coming from the single zone SR501. ??
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Good question, the answer is no because for some reason, it was set for zone and not indirect though the house has indirect water heating. Should I switch it back to zone?
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I don't believe so. I replaced everything exactly as shown from the previous Hydrostat to this new one. It appears the Hydrostat is not the problem and I replaced it ($230) for nothing.
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Sorry
Sorry if this was not clear. System has 5 heating zones (5 circ pumps) and 1 indirect heating zone w/storage tank. Per my separate post, the indirect heating has a separate Taco SR501 single zone control which I'm not sure if it is connected at all to the multi-zone SR506. The reason I don't think it is, because the SR506 Zone 6 (Priority Zone for indirect hot water) has no wire(s) on top in the thermostat section or down below in the circ pump section. Could the Hydrostat dot (constant call for heat) be coming from the single zone SR501 since after removing the ZC/ZR wires, the dot disappears?
Turns out the SR501 single zone hot water has it's own power switch. When I turn that off, the Hydrostat dot turns off leading me toward the indirect hot water SR501 or hot water storage tank thermostat. On the SR501, I removed the R and W wires. Reading online that if the red line turns off after removing those wires, it's likely the thermostat which is a Residio L 4080 B 1352 that continuously is calling for hot water. Any ideas how to troubleshoot the thermostat?
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Often they use the priority function of the SR506 for DHW rather than a separate relay. The priority shuts off other heat loads on the boiler during DHW use so you don't run out of DHW.
The Residio L 4080 B 1352 is just a simple thermal switch. If the water in the indirect tank is plenty hot enough and the thermal switch in the L 4080 B 1352 does not open it may be bad.
Sounds like the L 4080 B 1352 controls the SR501. The SR501 controls a circulator for the indirect tank and calls the Hydstrostat 3250's ZC/ZR which bypasses the Thermal Targeting function for fast indirect recovery.
is the I / Z switch now in the same position as the old unit ?
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System0 -
This is the wiring that should be used. XX in the SR506 to TT on the Hydrostat. ZR/ZC on the Hydrostat to 5/6NO on the SR501 for the water heater.
The wires on the aquastat for the water heater should go to TT on the SR501.
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sounds like you agree that the IWH Aquastat thermostat is the likely culprit. Yes, Indirect switch on the Hydrostatic is same as original which is Zone not indirect. The call for heat dot is in either setting. As mentioned, the ZC ZR terminals are jumped in the Taco 6 zone which tells me it’s not used.
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It’s wired exactly as you mentioned which leads me back to the aquastat thermostat on the IHW holding tank. When those wires are disconnected from the SR501, call for heat dot turns off on the Hydrostat temp control.
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With the DHW running, is the supply pipe coming out of the indirect tank sufficiently hot ? What I am getting at is the tank not being heated correctly or is the aquastat bad.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System0 -
i think we are missing a photo of how the other relay is wired, and where the zc/zr wires are coming from
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since something along the DHW line is triggering a constant call for heat and the Hydrostat is set for high 180, yes plenty hot water.
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The ZC/ZR wires on the Hydrostat 3250-Plus go to the N/O 6 and Com 5 terminals in the single zone DHW Taco SR501. The R & W wires in the SR501 go to the tank thermostat. When disconnected from the SR501, the call for heat at the Hydrostat turns off. This is why I suspect the thermostat attached to the Burnham Alliance SL35 HW holding tank.
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depending on which exact sr501 you have its not wired correctly to the boiler, RW are for your thermostat to wire into
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My apologies and of course you are 100% right. I corrected my text that you replied to. The ZC/ZR are connected to the 6 and 5 terminals bottom right on the SR501 and the R/W are connected to the thermostat which when disconnected, turns off the call for heat on the Hydrostat temp control at the boiler.
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then that makes sense, if you are disconnecting the aquastat, or thermostat and it turns off the call it sounds like that device is stuck always calling. I am wondering though, if the aquastat calls for heat constantly the DHW in the tank must be getting way too hot correct? as @109A_5 was suggesting, if the aquastat calls 100% of the time and never satisfies then the tank will either overtemp considerably (bad aquastat) or the tank is actually below temperature and there is a system related issue. if you have a mixing valve on the DHW side of the indirect you may not notice the overtemperature at the faucets, and since you have plenty of hot water to use it seems like the aquastat, or whatever is controlling the tank temperature is faulty, or otherwise reading incrorrectly.
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Yes there appears to be a mixing valve though I can't see a cold water line going to or through it. Here's a pic. The high temp setting on the tank thermostat has been set to 140 which seems fairly standard. The high temp setting on the boiler Hydrostat is 180, also standard for the house heating.
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the pipe connected at the top of the valve as we view the picture is the cold line, the line coming out the side as we view it, with the gauge is the mix out. looks pretty normal overall at a glance, I would be investigating the aquastat
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Right, thanks. I looked at the aquastat again and noticed it was set for 160-165 range. Since the Hydrostat at the boiler is set for 180 high with a 20 degree low, the aquastat was constantly calling for heat. I turned the aquastat down to 140 which I read is a good high number to eliminate bacteria and not too hot for standard hot water and now the constant call for heat is gone indicating the aquastat is in fact working properly. I'm now waiting for the boiler to drop in temp to below the -10 where the aquastat should trigger a call to heat and bring it back to 140. If that runs correctly, everything should be set properly and working though I want to then check each heating zone individually for calls for heat. Very appreciative for this forum and everyone who had responded.
I'm wondering why the original installers I hired years ago would set the aquastat to 160-165 deg when standard is 140. Wasted a bunch of oil over the years I'm thinking.
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So If I understand correctly it appears that there was never an actual problem with the equipment, just an aquastat setting, which has been that way for quite some time.
Maybe it was set high on purpose to compensate for no DHW priority.
The thing is, if that is so and you turned down the aquastat to 140 degrees you may now run short with DHW since there is no actual DHW priority. The Hydstrostat 3250's ZC/ZR which bypasses the Thermal Targeting function for fast indirect recovery may help but it may not be enough in the coldest part of the winter.
You will have to see if your DHW is still sufficient. If not you may have to do some rewiring to leverage the DHW priority function of the SR506.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System0 -
I would personally think it will be fine. The tank probably never reached 165, or very rarely at best. someone probably thought that was a supply temp they were setting, or just accidentally set it. seems like it was not intentional since the SR501 never needed to be there. If you notice reduced DHW temps I would fiddle with the mix valve first before changing any wiring. but I still bet it will be just fine, and maybe save a little fuel.
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I've got a theory about the controls, just a theory not like we can ever prove it. Someone set that aquastat to 165 thinking it was a supply temp setting, they had it wired as priority on the 6 zone relay, but then the boiler would never satisfy the tank. The relay remained in priority and a service tech who didn't know they could just deactivate priority added the single zone relay to allow both space heating and DHW simultaneously. nobody ever thought to check the aquastat because the water from the faucet was consistent (thank you mixing valve) The tank never (or rarely) could reach the 165 setpoint because the boiler was hitting 180 and shutting down the burner until 160 , the tank and supply would sort of equalize temperatures until either a DHW draw, or a space heating call.
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Yes, that makes perfect sense though if the Hydrostat is set to Indirect (I) and the ZR/ZC is connected to the single zone DHW Taco SR501-4, why wouldn't that prioritize hot water over heat via the Hydrostat?
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Yes, I think there would definitely be fuel savings, particularly in warmer months (we live in the NE). Do mixing valves automatically add cold water to prevent the HW temp going to the house from above a safe temp?
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We do have proof in that I had the original Weil-Mclean boiler replaced along with all the circs and I believe they did the panels (both) at that time too. What isn't really clear is why they installed the SR501-4 single zone panel when there is space in the SR506 Zone 6 Priority designed specifically for IHW. It's there, why not use it?
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Thanks again, what an amazing community to help me troubleshoot this issue. You guys are the best. I learned a lot about the system from you and the research.
The way it's set now, unless there's a call for house heat, the IWH will call for heat when the tank temp drops to around 125+/- and then turn off that call when the water reaches 140 inside the tank. The Hydrostat is set for I which I would have thought creates priority for the IHW if needed but will only maintain range 160-180 deg if house heating calls are running.
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